The invention relates to a tool which may be employed in a lathe to make internal circumferential ribs in small diameter, thin-walled tubing.
Previous methods of forming circumferential ribs in tubing include three-roll forming, explosive or electrohydraulic forming, electromagnetic forming, hydraulic forming, press methods and rotary swaging. (See the Metals Handbook, Volume 4, Forming, 8th Edition, 1969, American Society for Metals, Metals Park, Ohio.) However, all of these methods entail disadvantages not incurred by the present invention. For example, three-roll forming requires starting the process with a plate and is generally limited to tube diameters larger than that encompassed by the present invention. Also, rotary swaging is generally limited to tubes with a final wall thickness of 0.025 inch or greater; the present invention provides for wall thicknesses at least as small as 0.015 inch. All of these methods except three-roll forming require the preparation of dies or mandrels or both for making ribs. The use of a die or mandrel, of course, means that for each variation or rib depth, number of ribs per unit length of tubing or different size tubings a new die or mandrel must be prepared. The present invention operated entirely without the use of dies or mandrels; only a low melting point plastic tooling compound is used to give some additional support to the tube and maintain its diameter. Furthermore, the present invention operates without lubricants on the workpiece. Additionally, hydraulic forming is limited mostly to more ductile materials, such as copper, than are encompassed by the present invention. Finally, electromagnetic forming would require the use of a driver due to the relatively low conductance of stainless steel as compared to aluminum, copper, etc. The ability of the present invention to function without the use of dies or mandrels also means that the expense for small lots of identical tubes will be decreased in comparison to methods utilized by the prior art.